Sunscreen compositions must fulfill a number of requirements to be effective. First, they must absorb the appropriate wavelengths of ultraviolet radiation to prevent sunburn and other forms of cellular damage and aging of the skin. Second, they must be stable, safe, and non-irritating to skin. Third, because sunscreen compositions are most often used for several hours at a time in bright sunlight, near water, or under conditions where perspiration is induced, the compositions must be resistant to water and ultraviolet (UV) light. A background on the contents and function of sunscreens is provided in Kirk-Othmer Encyclopedia of Chemical Technology, 3rd Ed., Vol. 7, pages 152 to 154, which is hereby incorporated herein by reference.
Many commercial sunscreen products and their ingredients are known to provide reduced protection after being in use for a period of time. Thus, protection is reduced precisely when it is most needed to counteract long exposure to sunlight. It is also known that dyes will photobleach under sunlight.
Many known sunscreen compositions are made water-resistant by combining an ultraviolet light absorbing active ingredient with a skin substantive resin as a vehicle. Such vehicles cover the active ingredient on the surface of the skin. The regulatory monograph "Sunscreen Drug Products For Over-The-Counter Human Drugs", published by the FDA in the Federal Register on Aug. 5, 1978, warns of the risk of occlusively driving the active ingredient into the skin, causing irritation or other toxic reactions. (This monograph is hereby incorporated by reference in its entirety herein.) Decomposition of active UV absorbers may produce irritating and otherwise unsafe by-products which likewise may be absorbed through the skin, and the irritation potential of some active ingredients themselves has recently been demonstrated.
The prior art teaches stable oil-in-water emulsions for cosmetic use. One of many emulsifiers suggested by the art for such emulsions is hydrogenated castor oil ethoxylated with 30 to 100 moles of ethylene oxide per mole of oil, combined with a water-soluble solvent. One of many known utilities for such emulsions is as a suntan preparation.
The prior art also discloses oil-in-water emulsions useful as skin lotions which contain a soap of glucamine and a fatty acid as a non-irritating emulsifying agent. One of many potential fatty acids is ricinoleic acid. Ricinoleic acid is derived from castor oil. One of many possible adjuvants mentioned in the prior art for use with the emulsions is a sunscreen.
Polyethoxylated castor oil has been disclosed to be useful as a solubilizer for liquid soap, as a skin moisturizer, and for degreasing pig skin.